We will characterize the mechanism by which the binding of cholinergic agonists to the nicotinic cholinergic receptor causes a change of permeability of the post-synaptic membrane. Post-synaptic membranes will be isolated from Torpedo electric tissue. Direct measurement of the kinetics of binding of (3H)-acetylcholine and other cholinergic ligands to these membranes will be used to identify different receptor conformations. A comparison between the dynamics of ligand binding and the permeability response will be made to identify the receptor conformations associated with channel activation and densensitization. The action of drugs such as local anesthetics and other non-competitive antagonists will be studeid to determine the mechanism by which they modify the cholinergic response. A specific local anesthetic binding site has been identified in the isolated post-synaptic membrane and studies will be carried out to identify the location of that site in relation to the cholinergic receptor. The role of Ca ions in the regulation of the post-synaptic response will be studied, and the role of the membrane lipids will be analyzed both by the use of lipid perturbants and by a selective modification of the lipid composition of the post-synaptic membranes. Fluorescence techniques will be used to identify structural changes of the membranes associated with the permeability response and to monitor the dynamics of ligand binding to the isolated membranes.